1. Field of the Invention
This invention is related to 2-substituted piperidine analogs. The analogs are selectively active as antagonists of N-methyl-D-aspartate (NMDA) receptor subtypes. The invention is also directed to the use of 2-substituted piperidine analogs as neuroprotective agents for treating conditions such as stroke, cerebral ischemia, central nervous system trauma, hypoglycemia, anxiety, convulsions, aminoglycoside antibiotics-induced hearing loss, migraine headaches, chronic pain, glaucoma, CMV retinitis, psychosis, urinary incontinence, opioid tolerance or withdrawal, or neurodegenerative disorders such as lathyrism, Alzheimer""s Disease, Parkinsonism and Huntington""s Disease.
2. Related Background Art
Excessive excitation by neurotransmitters can cause the degeneration and death of neurons. It is believed that this degeneration is in part mediated by the excitotoxic actions of the excitatory amino acids (EAA) glutamate and aspartate at the N-methyl-D-Aspartate (NMDA) receptor. This excitotoxic action is considered responsible for the loss of neurons in cerebrovascular disorders such as cerebral ischemia or cerebral infarction resulting from a range of conditions, such as thromboembolic or hemorrhagic stroke, cerebral vasospasms, hypoglycemia, cardiac arrest, status epilepticus, perinatal asphyxia, anoxia such as from drowning, pulmonary surgery and cerebral trauma, as well as lathyrism, Alzheimer""s Disease, Parkinson""s Disease and Huntington""s Disease.
Excitatory amino acid receptor antagonists that block NMDA receptors are recognized for usefulness in the treatment of disorders. NMDA receptors are intimately involved in the phenomenon of excitotoxicity, which may be a critical determinant of outcome of several neurological disorders. Disorders known to be responsive to blockade of the NMDA receptor include acute cerebral ischemia (stroke or cerebral trauma, for example), muscular spasm, convulsive disorders, neuropathic pain and anxiety, and may be a significant causal factor in chronic neurodegenerative disorders such as Parkinson""s disease [T. Klockgether, L. Turski, Ann. Neurol. 34, 585-593 (1993)], human immunodeficiency virus (HIV) related neuronal injury, amyotrophic lateral sclerosis (ALS), Alzheimer""s disease [P.T. Francis, N. R. Sims, A. W. Procter, D. M. Bowen, J. Neurochem. 60 (5), 1589-1604 (1993)] and Huntington""s disease. [See S. Lipton, TINS 16 (12), 527-532 (1993); S. A. Lipton, P. A. Rosenberg, New Eng. J. Med. 330 (9), 613-622 (1994); and C. F. Bigge, Biochem. Pharmacol. 45, 1547-1561 (1993) and references cited therein.]. NMDA receptor antagonists may also be used to prevent tolerance to opiate analgesia or to help control withdrawal symptoms from addictive drugs (Eur. Pat. Appl. 488,959A).
U.S. Pat. No. 5,352,683, discloses the treatment of chronic pain with a compound with is an antagonist of the NMDA receptor.
U.S. Pat. No. 4,902,695, discloses certain competitive NMDA antagonists that are useful for the treatment of neurological disorders, including epilepsy, stroke, anxiety, cerebral ischemia, muscular spasms, and neurodegenerative diseases such as Alzheimer""s disease and Huntington""s disease.
U.S. Pat. No. 5,192,751 discloses a method of treating urinary incontinence in a mammal which comprises administering an effective amount of a competitive NMDA antagonist.
Evidence indicates that the NMDA receptor comprises a class of such receptors with different subunits. Molecular cloning has revealed the existence of at least five subunits of the NMDA receptors designated NR1 and NR2A through 2D. It has been demonstrated that the co-expression of NR1 with one of the NR2 subunits forms a receptor with a functional ion channel. (Ann. Rev. Neurosci. 17:31-108(1994)). It is thought that NMDA receptors with different subunit composition generate the different NMDA receptor subtypes found in the mammalian brain.
An object of this invention is to provide novelxe2x80x94subtype-selective NMDA receptor ligands.
The invention relates to a subtype-selective NMDA receptor ligand having the Formula (I): 
wherein
R1-R4 are independently hydrogen, halo, haloalkyl, aryl, fused aryl, a heterocyclic group, a heteroaryl group, alkyl, alkenyl, alkynyl, arylalkyl, arylalkenyl, arylalkynyl, hydroxyalkyl, nitro, amino, cyano, cyanamido, N(CN)2, guanidino, amidino, acylamido, hydroxy, thiol, acyloxy, azido, alkoxy, carboxy, carbonylamido, or alkylthiol;
E is (CRaRb)rxe2x80x94Gsxe2x80x94(CRcRd)t, wherein Ra, Rb, Rc and Rd are independently selected from the group consisting of hydrogen, alkyl, aryl, hydroxy or carboxy; G is oxygen, sulfur, sulfone, sulfoxide, carboxy (CO2 or O2C), carbonyl (CO), or NRe, wherein Re is hydrogen, alkyl or aryl; r and t are independently 0, 1, 2, 3, 4, or 5; and s is 0 or 1;
R5 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group;
p is 0, 1, 2, or 3;
Y is hydrogen, hydroxy, CH3, CN, CO2R, sulfate, optionally substituted aryl, optionally substituted aryloxy, optionally substituted arylthioxy, optionally substituted aroyl, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1 (which may be cis or trans, throughout) carbonylamido, hydrazino, oximo, amidino, optionally substituted heterocyclic group, optionally substituted heterocycloxy, optionally substituted heteroaryl, optionally substituted heteroaryloxy, optionally substituted cycloalkyl group, optionally substituted cycloalkoxy group, amino, amido, ureido, or guanidino; and
Y1 is hydrogen, alkyl, hydroxyalkyl, optionally substituted aralkyl, an optionally substituted aryl, optionally substituted cycloalkyl, aminoalkyl, amidoalkyl, ureidoalkyl, or guanidinoalkyl.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (II): 
wherein
R1-R4, E, Y and Y1 are the same as described in formula I;
R5 is hydrogen, lower alkyl, acyl or aryl;
p is 0, 1, 2 or 3; and
R6 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group; and
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (IIa): 
wherein
R1-R4, E, Y and Y1 are the same as described in formula I;
R5 is hydrogen, lower alkyl, acyl or aryl;
p is 0, 1, 2 or 3; and
R5 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (III): 
wherein
W is an adamantyl group, an optionally substituted aryl group, or an optionally substituted heteroaryl group;
X is a bond, (CH2)m carbonyl, oxygen, or NR;
E is the same as described in formula I;
Y is hydrogen, hydroxy, CH3, CN, CO2R; an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
R is hydrogen, alkyl, aminoalkyl, amidoalkyl, ureidoalkyl, or guanidinoalkyl;
R1 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group;
m is 0, 1, 2, or 3; and
p is 0, 1, 2, 3 or 4.
with the proviso, that when W is adamantyl or when p is greater than zero, or when the piperidine is substituted in the 3-position by W-X, then Y may also be optionally substituted aryl, optionally substituted aryloxy, optionally substituted arylthioxy, optionally substituted aroyl, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, optionally substituted heterocyclic group, optionally substituted heterocycloxy, optionally substituted heteroaryl, optionally substituted heteroaryloxy, optionally substituted cycloalkyl group, optionally substituted cycloalkoxy group, amino, amido, ureido, or guanidino; wherein
Y1 is hydrogen, alkyl, hydroxyalkyl, optionally substituted aralkyl, optionally substituted aryl, optionally substituted cycloalkyl, aminoalkyl, amidoalkyl, ureidoalkyl, or guanidinoalkyl.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (IV): 
wherein
R1-R5 are independently hydrogen, halo, haloalkyl, aryl, fused aryl, a heterocyclic group, a heteroaryl group, alkyl, alkenyl, alkynyl, arylalkyl, arylalkenyl, arylalkynyl, hydroxyalkyl, nitro, amino, cyano, acylamido, hydroxy, thiol, acyloxy, azido, alkoxy, carboxy, carbonylamido, or alkylthiol; and
E, Y and Y1 are the same as described in formula I.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (V): 
wherein
R1-R4, E, Y and Y1 are the same as described in formula I.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (VI): 
wherein
W is an adamantyl group, an optionally substituted aryl group, or an optionally substituted heteroaryl group;
X is a bond, (CH2)m, oxygen, or NR;
E, Y and Y1 are the same as described in formula I;
R is alkyl, hydroxy, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
R1 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group;
m is 0, 1, 2, or 3; and
q is 0, 1 or 2.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (VII): 
wherein
W is an adamantyl group, an optionally substituted aryl group, or an optionally substituted heteroaryl group;
X is a bond, (CH2)m oxygen, or NR;
E, Y and Y1 are the same as described in formula I;
R is alkyl, hydroxy, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
R1 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group;
m is 0, 1, 2, or 3; and
p is 0, 1 or 2.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (VIII): 
wherein
W is an adamantyl group, an optionally substituted aryl group, or an optionally substituted heteroaryl group;
X is a bond, (CH2)m, oxygen, or NR;
E, Y and Y1 are the same as described in formula I; R is alkyl, hydroxy, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
R1 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group;
m is 0, 1, 2, or 3; and
p is 0, 1 or 2.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (IX): 
wherein
one of K and L is nitrogen and the other is CH; and
E, Y and Y1 are the same as described in Formula I.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (X): 
wherein
E, Y and Y1 are the same as described in formula I.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (XI): 
wherein
E, Y and Y1 are the same as described in formula 1.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (XII): 
wherein
A and B are one or more substituents which are independently hydrogen, halo, alkoxy, trifluoromethylthio, cyano, carboxy or hydroxy;
R1 is alkyl, alkenyl, aralkyl, cycloalkyl-alkyl, dialkylaminoalkyl, or hydroxyalkyl; and
E, Y and Y1 are the same as described in formula I.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (XIII): 
wherein
R is hydrogen, C2-C6 acyl, C1-C6 alkyl, aryl, C1-C6 alkoxycarbonyl, C7-C10 aralkyl, C2-C6 alkenyl, C3-C15 dialkylaminoalkyl, C1-C6 hydroxyalkyl, C2-C6 alkynyl, C3-C15 trialkylsilyl, C4-C10 alkylcycloalkyl, or C3-C6 cycloalkyl;
A and B are independently selected from the group consisting of a halogen such as chloro, fluoro, bromo, iodo, trifluoromethyl, azido, C1-C6 alkoxy, C2-C6 dialkoxymethyl, C1-C6 alkyl, cyano, C3-C15 dialkylaminoalkyl, carboxy, carboxamido, C1-C6 haloalkyl, C1-C6 haloalkylthio, allyl, aralkyl, C3-C6 cycloalkyl, aroyl, aralkoxy, C2-C6 acyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, C5-C6 heterocycloalkyl, C1-C6 alkylthio, C1-C6 alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, arylthio, C1-C6 haloalkoxy, amino, C1-C6 alkylamino, C2-C15 dialkylamino, hydroxy, carbamoyl, C1-C6 N-alkylcarbamoyl, C2-C15 N,N-dialkylcarbamoyl, nitro and C2-C15 dialkylsulfamoyl;
Z represents a group selected from 
wherein R1 is hydrogen, C1-C6 alkyl, C2-C6 alkenyl, aralkyl, C4-C15 dialkylaminoalkyl, heterocycloalkyl, C2-C6 acyl, aroyl, or aralkanoyl, and R3 is C1-C6 alkyl, C2-C6 alkenyl, phenyl, aralkyl or C3-C15 dialkylaminoalkyl; and
f and g are independently integers selected from 0 (X or Y is hydrogen, respectively), 1, 2, 3, or 4; and
E, Y and Y1 are the same as described in formual I.
The invention also relates to a subtype-selective NMDA receptor ligand having the Formula (XIV): 
wherein
R1 is carboxy or an alkylester or amide thereof; alkyl carboxy or an alkyl ester or amide thereof; hydroxy or hydroxymethyl group;
p is 0, 1 or 2;
the dotted line represents a single or double bond;
E, Y and Y1 are the same as described in formula I.
The invention relates to a subtype-selective NMDA receptor ligand having the Formula (XV): 
wherein
R1-R4, E, Y and Y1 are the same as described in formula I;
R6 is hydrogen, hydroxy, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group; and
p is 0, 1, 2, or 3.
The invention relates to a subtype-selective NMDA receptor ligand having the Formula (XVI): 
wherein Ar1 is optionally substituted aryl or optionally substituted heteroaryl;
X is O, NR1 or (CH2)n wherein n is 0, 1, 2, 3 or 4 and R1 is hydrogen or a lower alkyl group having 1 to 6 carbon atoms;
U is hydroxy or hydrogen;
Y is (CH2)m wherein m is 1,2 or 3;
Z is (CHR2)Z wherein z is 0, 1, 2, 3 or 4 and R2 is hydroxy, hydrogen or a lower alkyl group having 1 to 6 carbon atoms; and
A and B are each hydrogen or together are (CH2)w wherein w is 0, 1, 2, 3 or 4.
Preferred substituents of Ar1 include, for example, hydrogen, alkyl, a halogenated alkyl group such as a trifluoromethyl group, halogen, nitro, aryl, aralkyl, amino, a lower alkyl amino group or a lower alkoxy group.
The invention relates to a subtype-selective NMDA receptor ligand having the Formula (XVII): 
wherein
Ar1 is optionally substituted aryl or optionally substituted heteroaryl;
X is O, NR1 or (CH2)n wherein n is 0, 1, 2, 3 or 4 and R1 is hydrogen or a lower alkyl group having 1 to 6 carbon atoms;
U is hydroxy or hydrogen;
Z is (CHR2)z wherein z is 0, 1, 2, 3 or 4 and R2 is hydroxy, hydrogen or a lower alkyl group having 1 to 6 carbon atoms;
Q is xe2x80x94CHxe2x95x90CHxe2x80x94or xe2x80x94Cxe2x89xa1Cxe2x80x94;
R3 is hydrogen, hydroxy or hydroxy substituted lower alkyl having 1 to 6 carbon atoms; and
Y is hydrogen, hydroxy, optionally substituted aryl or optionally substituted heteroaryl.
Preferred substituents of the aryl and heteroaryl groups include, for example, hydrogen, alkyl, a halogenated alkyl group such as a trifluoromethyl group, halogen, nitro, aryl, aralkyl, amino, a lower alkyl amino group or a lower alkoxy group.
The invention also relates to the quaternary ammonium salts of any one of the compounds above obtained by reacting the compound with a lower alkyl halide, preferable, methyl iodide or methyl sulfate.
The invention also relates to a method of treating or preventing neuronal loss associated with stroke, ischemia, CNS trauma, hypoglycemia and surgery, as well as treating neurodegenerative diseases including Alzheimer""s disease, amyotrophic lateral sclerosis, Huntington""s disease, Parkinson""s disease and Down""s syndrome, treating or preventing the adverse consequences of the overstimulation of the excitatory amino acids, treating anxiety, psychosis, convulsions, chronic pain, glaucoma, CMV retinitis, urinary incontinence, and inducing anesthesia, as well as enhancing cognition, and preventing opiate tolerance and withdrawal symptoms, comprising administering to an animal in need of such treatment an effective amount of any one of the subtype-selective NMDA receptor ligands of the present invention, or a pharmaceutically acceptable salt thereof.
The present invention relates to the discovery of new compounds which are subtype-selective ligands of the NMDA receptor. There are a number of subtypes of the NMDA receptor including NR1A/2A, NR1A/2B, NR1A/2C and NR1A/2D. The discovery of ligands which are selective for one or more of these subtypes allows for the treatment of various conditions mediated through binding to the NMDA receptor, while minimizing unwanted side effects.
Electrophysiological assays may be utilized to characterize the actions of potential subtype-selective ligands at NMDA receptors expressed in Xenopus oocytes. The ligand may be assayed at the different subunit combinations of cloned rat NMDA receptors corresponding to the four putative NMDA receptor subtypes (Moriyoshi et al., Nature (Lond.) 354:31-37 (1991); Monyer et al., Science (Washington, D.C.) 256:1217-1221 (1992); Kutsuwada et al., Nature (Lond.) 358:36-41 (1992); Sugihara et al., Biochem. Biophys. Res. Comm. 185:826-832 (1992)).
Using fixed saturating concentrations of agonists (glutamate 100 xcexcM, glycine 1-10 xcexcM depending on subunit combination), the inhibitory potency of a putative subtype-selective ligand may be assayed at the NMDA receptors assembled from NR1A/2A, NR1A/2B, NR1A/2C and NR1A/2D subunit combinations.
Preferably, the subtype selective NMDA receptor ligands are limited efficacy NMDA receptor antagonists. Such limited efficacy antagonists are attractive because such drugs have built-in safety margins; no matter how high the dosage only a certain fraction of the response can be blocked. This could be particularly important for analgesic, anticonvulsant, anti-psychotic, antimigraine headache, antiparkinson""s disease and antiglaucoma indications, where overdosage of full antagonists may result in sedation. It is also likely that limited efficacy NMDA receptor antagonists, particularly those showing subtype-selectivity, will not induce such profound memory deficits as full antagonists.
Certain of the subtype-selective NMDA receptor ligands are expected to be able to mediate either inhibition or potentiation of membrane current response. Which type of effect predominates appears to be dependent upon the subunit composition of the receptors and on the structure of the molecule. The 1A/2A and 1A/2B subtypes are mainly in the forebrain. The 1A/2C and 1A/2D are mainly in the cerebellum. In addition to the potential of developing subtype-selective drugs for the treatment of diseases associated with the overstimulation of the NMDA receptor with few side effects, it is also possible to develop drugs that selectively potentiate particular subtypes of NMDA receptors present in particular parts of the brain. Such drugs could show therapeutic potential as cognitive-enhancers in treatments of neurodegenerative conditions such as Alzheimer""s disease. In addition, there is a potential for developing drugs that selectively potentiate some subtypes of NMDA receptors while simultaneously having inhibitory effects at other subtypes. Such compounds could be important for adjusting imbalances in subtype activity and may have therapeutic potential as psychotropic agents.
Compounds that are useful for treating or preventing the adverse consequences of stroke, hypoglycemia, neurodegenerative disorders, anxiety, epilepsy or psychosis, or that induce analgesia, will inhibit the currents across the membranes of the oocyte expressing various subtype NMDA receptors. However, if the compound potentiates currents across the oocyte membrane, then the compound is expected to be useful in enhancing cognition.
With respect to Formulae I-XVII, above:
Typical C6-14 aryl groups include phenyl, naphthyl, phenanthryl, anthracyl, indenyl, azulenyl, biphenyl, biphenylenyl and fluorenyl groups.
Typical halo groups include fluorine, chlorine, bromine and iodine.
Typical C1-4 alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, sec.-butyl, and tert.-butyl groups. Also contemplated is a trimethylene group substituted on two adjoining positions on any benzene ring of the compounds of the invention.
Typical C2-4 alkenyl groups include ethenyl, propenyl, isopropenyl, butenyl, and sec.-butenyl.
Typical C2-4 alkynyl groups include ethynyl, propynyl, butynyl, and 2-butnyyl groups.
Typical arylalkyl groups include any of the above-mentioned C1-4 alkyl groups substituted by any of the above-mentioned C6-14 aryl groups.
Typical arylalkenyl groups include any of the above-mentioned C2-4 alkenyl groups substituted by any of the above-mentioned C6-14 aryl groups.
Typical arylalkynyl groups include any of the above-mentioned C2-4 alkynyl groups substituted by any of the above-mentioned C6-14 aryl groups.
Typical haloalkyl groups include C1-4 alkyl groups substituted by one or more fluorine, chlorine, bromine or iodine atoms, e.g., fluoromethyl, difluoromethyl, trifluoromethyl, pentafluoroethyl, 1,1-difluoroethyl and trichloromethyl groups.
Typical hydroxyalkyl groups include C1-4 alkyl groups substituted by hydroxy, e.g., hydroxymethyl, hydroxyethyl, hydroxypropyl and hydroxybutyl groups.
Typical alkoxy groups include oxygen substituted by one of the C1-4 alkyl groups mentioned above.
Typical alkylthio groups include sulphur substituted by one of the C1-4 alkyl groups mentioned above.
Typical acylamino groups include any C1-6 acyl (alkanoyl) substituted nitrogen, e.g., acetamido, propionamido, butanoylamido, pentanoylamido, hexanoylamido as well as aryl-substituted C2-6 substituted acyl groups.
Typical acyloxy groups include any C1-6 acyloxy groups, e.g., acetoxy, propionoyloxy, butanoyloxy, pentanoyloxy, hexanoyloxy and the like.
Typical heterocyclic groups include tetrahydrofuranyl, pyranyl, piperidinyl, piperizinyl, pyrrolidinyl, imidazolindinyl, imidazolinyl, indolinyl, isoindolinyl, quinuclidinyl, morpholinyl, isochromanyl, chromanyl, pyrazolidinyl and pyrazolinyl groups.
Typical heteroaryl groups include any one of the following which may be optionally substituted with one or more alkyl, halo, or hydroxy groups: thienyl, benzo[b]thienyl, naphtho[2,3-b]thienyl, thianthrenyl, furyl, pyranyl, isobenzofuranyl, chromenyl, xanthenyl, phenoxathiinyl, 2H-pyrrolyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, indolizinyl, isoindolyl, 3H-indolyl, indolyl, indazolyl, purinyl, 4H-quinolizinyl, isoquinolyl, quinolyl, phthalazinyl, naphthyridinyl, quinazolinyl, cinnolinyl, pteridinyl, 4aH-carbazolyl, carbazolyl, xcex2-carbolinyl, phenanthridinyl, acridinyl, perimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl, phenothiazinyl, isoxazolyl, furazanyl phenoxazinyl groups, 1,4-dihydroquinoxaline-2,3-dione, 7-amino isocoumarin, pyrido[1,2-a]pyrimidin-4-one, 1,2-benzoisoxazol-3-yl, benzimidazolyl, 2-oxobenzimidazolyl, 2-oxindolyl and 4-nitrobenzofurazan.
Where the heteroaryl group contains a nitrogen atom in a ring, such nitrogen atom may be in the form of an N-oxide, e.g., a pyridyl N-oxide, pyrazinyl N-oxide, pyrimidinyl N-oxide and the like.
Typical amino groups include xe2x80x94NH2, xe2x80x94NHR14, and xe2x80x94NR14R15, wherein R14 and R15 are C1-4 alkyl groups as defined above.
Typical carbonylamido groups are carbonyl groups substituted by xe2x80x94NH2, xe2x80x94NHR14, and xe2x80x94NR14R15 groups as defined above.
When the group is an amidino or guanidino group, any one of the nitrogen atoms may be substituted, e.g., 
where each R is independently hydrogen, alkyl, or aryl.
Optional substituents on the aryl, aryloxy, arylthioxy, aroyl, heterocyclic, heterocycloxy, heteroaryl, heteroaryloxy, cycloalkyl, and cycloalkoxy groups listed above include any one of the typical halo, haloalkyl, aryl, fused aryl, heterocyclic, heteroaryl, alkyl, alkenyl, alkynyl, arylalkyl, arylalkenyl, arylalkynyl, hydroxyalkyl, nitro, amino, cyano, acylamido, hydroxy, thiol, acyloxy, azido, alkoxy, carboxy, carbonylamido, and alkylthiol groups mentioned above.
In the compounds having the above formulae, the group E is a linker group between the nitrogen, e.g., piperidine nitrogen, and the terminal group Y. Excluded from such Formulae are where two heteroatoms are adjacent to one another such that an unstable compound would be produced. Such adjacent heteroatoms include xe2x80x94Oxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94Sxe2x80x94(divalent sulfur), xe2x80x94Nxe2x80x94Sxe2x80x94(divalent sulfur), xe2x80x94Sxe2x80x94Oxe2x80x94(divalent sulfur), and xe2x80x94Sxe2x80x94Nxe2x80x94(divalent sulfur). Hydrazine groups (xe2x80x94Nxe2x80x94Nxe2x80x94) are contemplated as possible linkers. Preferably, the group E is an optionally substituted methylene linker. Most preferably, the group E is a methylene linker (CH2)n, wherein n is 1, 2, 3, 4, 5 or 6.
Preferably, the group Y is an N-hydroxyalkylpiperidinyl (e.g., hydroxypropyl) group, which is expected to provide a reduction in affinity to the a, receptor, thereby resulting in less hypotension when the compounds are administered to animals. See, Gifford, R. W. et al., Arch. Intern. Med. 153:154-183 (1993). Alternatively, a halo group such as a p-chlorophenyl group may be employed to give compounds having a prolonged in vivo activity.
Compounds having Formula I may be prepared by reaction of an appropriately substituted 1,2,3,4-tetrahydroisoquinoline with a suitable electrophile in an aprotic solvent such as toluene or acetonitrile. The starting 1,2,3,4-tetrahydroisoquinoline may be prepared by the Pictet-Spenger method described in Org. Reactions 6:151-206 (1951). Optionally, a base such as potassium carbonate or pyridine may be added. Examples of suitable electrophiles include, for example, an alkyl, alkenyl, alkynyl, aralkyl, aryloxyalkyl, or heteroaralkyl halide, sulfate, sulfonate, or isocyanate. Specific examples of such electrophiles include ethyl 3-bromoethoxyphenyl acetate, methyl 5-bromovalerate, ethyl 4-bromobutyrate, 3-butyn-1-methanesulfate, ethyl crotonate, 1-chloro-4-phenylbutane, 3-phenoxypropyl bromide, 4-chloro-4xe2x80x2-fluorobutyrophenone, 4-chlorobutyrophenone, 2-phenylethyl bromide, 1-bromo-3-phenylpropane, 3-phenoxypropyl bromide, g-bromo-phenetole, 3-phenoxypropyl bromide, 3-phenylpropyl bromide, 1,3-propanesulfone, phenylisocyanate, 4-nitrophenylisocyanate, allyl iodide, bromomethylcyclopropane, 3-bromo-1-propanol, and 5-bromovaleronitrile.
A general procedure for reaction of the piperidine-containing compound with an alkyl chloride, bromide, tosylate or mesylate involves forming a mixture of a free base of the amino derivative and an alkyl chloride or bromide in toluene, acetonitrile, DMF, acetone or ethanol, in the presence of NaI. The reaction may be refluxed for 1-10 h then cooled to room temperature, filtered and washed with hexane. The filtrate is evaporated, and the residue chromatographed over silica gel to give the product. If the product is a solid, it may be crystallized, for example, from hexane or hexane-ethyl acetate. If the product is an oil, it may be dissolved in acetone and 4N HCl solution in 1,4-dioxane or concentrated HCl may be added until the mixture becomes strongly acidic (pH less than 2). It may then be rota-evaporated, and co-evaporated until a solid residue is obtained. The solid may then be recrystallized from acetone to give the hydrochloride. Alternatively, the hydrobromide or other acid addition salts may be prepared by substitution of, for example, HBr or maleic acid for HCl.
Examples of compounds having Formula I include those having the Formula (Ia): 
wherein
R1-R4 and R6-R10 are independently hydrogen, halo, haloalkyl, aryl, fused aryl, a heterocyclic group, a heteroaryl group, alkyl, alkenyl, alkynyl, arylalkyl, arylalkenyl, arylalkynyl, hydroxyalkyl, nitro, amino, cyano, acylamido, hydroxy, thiol, acyloxy, azido, alkoxy, carboxy, carbonylamido, or alkylthiol;
n is 1, 2, 3, or 4; and
V is CH2, oxygen, sulfur, or carbonyl (CO).
Other examples include those having the Formula (Ib): 
wherein
R1-R4 are the same as described for formula Ia; and
n is 1, 2, 3, 4, 5, or 6.
Other examples include those having the Formula (Ic): 
wherein
R1-R4 are the same as described for formula Ia; and
Y1 is alkyl, optionally substituted aryl, hydroxyalkyl, or optionally substituted alkaryl.
Other examples include those having the Formula (Id): 
wherein
R1-R4 are the same as described for formula Ia; and
n is 1, 2, 3, 4, 5, or 6.
Particular examples of compounds having Formula I include 
Compounds having Formula II may be prepared by reaction of an appropriately substituted 1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole with an electrophilic reagent as mentioned above. The starting 1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indoles may be prepared according to Abou-Gharbia et al., J. Med. Chem., 30:1818-1823 (1987) and Habert et al., J. Med. Chem., 23:635-643 (1980).
Particular examples of compounds having Formula II include 2-(2-phenoxyethyl)-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole, 2-(3-phenoxypropyl)-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole, 2-(3-phenylpropyl)-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole and 2-(3-hydroxypropy)-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole.
Compounds having Formula IIa can be prepared similar to II. Particular examples of compounds having Formula IIa are 
With regard to Formula III when p is  greater than 0, then the compounds may exist as a mixture of cis and trans isomers. The invention is directed to such cis and trans isomers as well as the individual enantiomers and diastereomeric mixtures.
When r is zero, G is NH and s is one, the N-amino piperidine compounds may be prepared according to Scheme 1: 
The N-amino piperidines may then be N-alkylated with one of the electrophiles listed above to give the compound of Formula III.
Also with regard to Formula III, when R1 is an optionally substituted 2-aryloxyalkyl or an optionally substituted 2-benzyloxyalkyl-piperidine, the compounds may be prepared according to Scheme 2: 
Scheme 2 may be generalized so that malonate A might be any of a variety of aryl or substituted benzyl malonates, for example, those shown below, leading to the corresponding derivatives in the scheme. Each of those piperidines may be alkylated with one or the other of the electrophilic reagents mentioned above. 
Scheme 3 depicts a route to some 2-substituted and 2,3-disubstituted-4-benzyl-4-hydroxypiperidines. A variety of electrophilic acylating agents may be used such that the final product 6 may have different substituents on the nitrogen atom. Also note that a variety of Grignard reagents or other nucleophiles can be used in the step 2xe2x86x923 so that the final product 6 may contain various substituents at the 2-position. Also note that a variety of alkylating agents can be used in the step 3xe2x86x924 so that the final product 6 will contain various substituents at the 3-position. Finally, the Grignard reagent in the step 4xe2x86x925 can be used. Also note that a variety of Grignard reagents can be used so that the final product 6 will contain various substituents at the 4-position. Alkylating agents may also include PhOCH2Br and PhCH2OCH2Br, for example. These would introduce oxygen atoms in the substituents at the various positions. Additionally, a high degree of stereocontrol can be achieved with the likely relative stereochemical outcomes shown. 
Other variations of this versatile synthetic approach are also possible (See, Scheme 4). Again, the benzyl group was originally introduced as a Grignard reagent so that can be varied (see 2xe2x86x923 above). The cuprate reagent can be varied as well as the final benzyl Grignard reagent. The net result of this chemistry is the preparation of 2,4,4,6-tetrasubstituted N-alkylpiperidines. 
One can also take advantage of the ortho lithiation of methoxy pyridines described by Comins, D. L., et al., Tetrahedron Lett. 29 (1988). Routes to novel piperidines are illustrated in Scheme 5 below. 
By choosing benzyl chloroformate as the initial electrophilic N-acylating agent, one can prepare a family of piperidines without a substituent on the nitrogen atom (Scheme 6). N-Phenoxycarbamates can be removed by catalytic hydrogenation with PtO2 in ethanol (see Comins, D. L. et al., Tet. Lett. 32:5697 (1991)).
Carbamates formed from other chloroformates can be removed from 2,3-dihydro-4-pyridones by treatment with bases such as sodium methoxide in methanol under reflux. Then, the electrophilic reagents mentioned above may be used to alkylate these piperidine nitrogens. Also note that a variety of electrophilic reagents can be used so that the final products 13 will contain various substituents at the 5-position. 
All of the above combinations can be readily made without the hydroxy substituent at C-4 of the piperidine as shown below via Wittig olefination of the piperidone followed by reduction (Scheme 7). 
In the transformation of 20 to 21 and 22 to 23, stereocontrol of the hydride reductions may be achieved by substituting other hydride reagents in place of LAH.
See, Comins, D. L., et al., J. Org. Chem. 55:2574 (1990), Comins, D. L., et al., Tetrahedron Lett. 29 (1988), and Comins, D. L., et al., J. Am. Chem. Soc. 116:4719 (1994).
An example of compounds having Formula III include those having Formula IIIa: 
where in
W is an adamantyl group or an optionally substituted aryl group;
Y is CH3, CN, CO2R, carboxamido, an optionally substituted cycloalkyl group or an optionally substituted heterocycloalkyl group;
R is alkyl, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
n is 0, 1, 2, 3, 4, 5, or 6; and
m is 0, 1, 2, 3;
with the proviso, that when W is adamantyl, then Y may also be optionally substituted aryl, optionally substituted aryloxy, SAr, COAr, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group; wherein
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group.
Generally, when Y is an aminoalkyl or guanidinoalkyl, n must be greater than 1.
In general, compounds having Formula III may be prepared by reaction of an appropriately substituted piperidine with one of the electrophilic reagents mentioned above. Where W is an adamantyl group, the compounds may be prepared as shown in Scheme 8. Preferably, such adamantyl groups are 1-adamantyl. 
Where W is a heteroaryl group, the compounds may be prepared using an aryl lithium or grignard reagent as shown in Scheme 9. 
Where Y is a 7-substituted isocoumarin, the compounds may be prepared as set forth in Scheme 10. 
See, Kerrigan et al., J. Med. Chem. 38:544 (1995) for methods of making such 7-substituted isocoumarins wherein the 7-substituent may be an amino group, a nitro group, or amido group.
Where Y is an optionally substituted cycloalkyl group or optionally substituted heterocycloalkyl group, and r, s and t are 0, the compounds may be prepared as shown in Scheme 11. 
Other cyclized analogs include compounds such as 33-36. 
Another example of compounds within the scope of Formula III includes compounds having the Formula IIIb: 
wherein
W is an adamantyl group or an optionally substituted aryl group;
Y is CH3, CN, CO2R, carboxamido, an optionally substituted cycloalkyl group or an optionally substituted heterocycloalkyl group;
R is alkyl, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
n is 0, 1, 2, 3, 4, 5, or 6; and
m is 0, 1, 2, or 3;
with the proviso, that when W is adamantyl, then Y may also be optionally substituted aryl, optionally substituted aryloxy, SAr, COAr, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group; wherein
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group.
Another example includes compounds having the Formula IIIc: 
wherein
W is an adamantyl group or an optionally substituted aryl group;
Y is CH3, CN, CO2R, carboxamido, an optionally substituted cycloalkyl group, an optionally substituted heterocycloalkyl group, optionally substituted aryl, optionally substituted aryloxy, SAr, COAr, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, an amino group, an amido group, a ureidoalkyl group, a guanidinoalkyl group, or Oxe2x80x94Nxe2x95x90CR1R2, where R1 and R2 are independently aryl or lower alkyl;
R is alkyl, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guinidinoalkyl group;
n is 0, 1, 2, 3, 4, 5, or 6; and
m is O, 1, 2, or 3;
with the proviso, that when W is adamantyl, then Y may also be optionally substituted aryl, optionally substituted aryloxy, SAr, COAr, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group; wherein
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group.
Another example includes compounds having the Formula IIId: 
wherein
W is an adamantyl group or an optionally substituted aryl group;
X is a bond, (CH2)m, oxygen, or NR;
Y1 is hydrogen, alkyl, hydroxyalkyl, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
R1 is hydrogen, hydroxy, halo, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group;
n is 0, 1, 2, 3, 4, 5, or 6; and
m is 0, 1, 2, or 3;
with the proviso that when W is an adamantyl group, then Y1 may further be an optionally substituted aralkyl group, or an optionally substituted aryl group.
Where the compounds having Formula IIId terminate with an alkyne (Y1=hydrogen), a propargylalcohol (Y=hydroxyalkyl), or propargylamine (Y1=aminoalkyl) residue, they may be prepared according to Scheme 12. 
Another example includes compounds having the Formula IIIe: 
wherein
W is an adamantyl group or an optionally substituted aryl group;
Y1 is hydrogen, alkyl, hydroxyalkyl, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
R1 is hydrogen, hydroxy, halo, alkylcarboxy, optionally substituted aryl, optionally substituted aralkyl, optionally substituted aryloxyalkyl, optionally substituted benzyloxyalkyl, a heterocyclic group, a heterocyclic substituted alkyl group, heteroaryl, or a heteroaryl substituted alkyl group;
n is 0, 1, 2, 3, 4, 5, or 6; and
m is 0, 1, 2, or 3;
with the proviso that when W is an adamantyl group, then Y1 may further be an optionally substituted aralkyl group, or an optionally substituted aryl group.
Another example includes compounds having the Formula IIIf: 
wherein
W, Y1, R1, n and m are the same as described in Formula IIIe;
with the proviso that when W is an adamantyl group, then Y1 may further be an optionally substituted aralkyl group, or an optionally substituted aryl group.
Another example includes compounds having the Formula IIIg: 
wherein
W, Y1, R1, n and m are the same as described in Formula IIIe;
with the proviso that when W is an adamantyl group, then Y1 may further be an optionally substituted aralkyl group, or an optionally substituted aryl group.
Another example includes compounds having the Formula IIIh: 
wherein
W is an adamantyl group or an optionally substituted aryl group;
Y is optionally substituted aryl, optionally substituted aryloxy, SAr, COAr, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group;
Y1 is hydrogen, alkyl, hydroxyalkyl, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
Z is (CH2)m, oxygen, sulfur, or NR;
m is 0, 1, 2, or 3; and
n is 1, 2, 3, 4, 5, or 6.
Examples of compounds having Formula IIIh include 3-benzyl-1-(3-phenoxypropyl)piperidine, 3-benzyl-1-(2-phenoxyethyl)piperidine, 3-benzyl-1-(2-phenethyl)piperidine, 3-benzyl-1-[2-(3-trifluoromethyl)phenethyl]piperidine, 3-benzyl-1-[2-(4-aminophenyl)ethyl]piperidine, 3-benzyl-1-[2-(4-chlorophenyl)ethyl]piperidine, 3-benzyl-1-[2-(4-fluorophenyl)ethyl]piperidine, and 3-benzyl-1-[2-(4-methoxyphenyl)ethyl]piperidine.
Another example includes compounds having the Formula (IIIi): 
wherein
R1-R5 are independently hydrogen, halo, haloalkyl, aryl, fused aryl, a heterocyclic group, a heteroaryl group, alkyl, alkenyl, alkynyl, arylalkyl, arylalkenyl, arylalkynyl, hydroxyalkyl, nitro, amino, cyano, acylamido, hydroxy, thiol, acyloxy, azido, alkoxy, carboxy, carbonylamido, or alkylthiol;
n is 1, 2, 3, 4, 5, or 6;
Y is optionally substituted aryl, optionally substituted aryloxy, SAr, COAr, hydrogen, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group; and
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group.
Compounds having Formula IIIi may be prepared by reaction of the 4-benzoylpiperidine with one of the electrophiles listed above.
Another example includes compounds having Formula (IIIj): 
wherein
R1-R5, n, Y and Y1 are the same as described for formula IIIi.
Another example includes compounds having the Formula (IIIk): 
wherein
R1-R5, n, Y and Y1 are the same as described in formula IIIi.
Another example includes compounds having the Formula (IIIl): 
wherein
W is optionally substituted aryl;
Y is optionally substituted aryl, optionally substituted aryloxy, an optionally substituted aryloxy group, SAr, COAr, hydrogen, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group;
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
Q is hydrogen, alkyl, aryl, aralkyl, a heterocyclic group, a heterocyclic substituted alkyl group, an aryl group, or an aralkyl group;
X is a bond, (CH2)m, oxygen, or sulfur;
m is 0, 1, 2, or 3;
n is 1, 2, 3, 4, 5, or 6; and
p is 0 or 1.
Another example includes compounds having the Formula (IIIm): 
wherein
W is optionally substituted aryl;
X is a bond, (CH2)m, oxygen, sulfur, or NR;
R is alkyl, hydroxy, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
R1 is hydrogen, hydroxy, aryl, or aralkyl;
n is 1, 2, 3, 4, 5, or 6;
xe2x95x90 single or double bond; and
=carbon ring or heterocyclic ring, with the proviso that said carbon ring is not part of a naphthyl group.
Compounds having Fomula IIIm may be prepared by a Diels-Alder reaction as shown below: 
Another example includes compounds having the Formula (IIIn): 
wherein
W is an adamantyl group or an optionally substituted aryl group;
X is a bond or (CH2)m;
Y is CH3, CN, CO2R; an optionally substituted aryl group, an optionally substituted aryloxy group, SAr, COAr, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group;
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group
R is alkyl, hydroxy, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group;
n is 0, 1, 2, 3, 4, 5, or 6; and
m is 0, 1, 2, or 3.
Compounds having Formula IIIn, where the group R1 is fluoro, may be prepared by reaction of the corresponding hydroxy piperidine with diethylaminosulfur trifluoride as shown in Scheme 13. 
See, Sharma, R. A.; Korytnyk, W.; Tetrahedron Lett 573 (1977); and Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis 6:183 (1977). 
An example of compounds having Formula IIIn includes: 
Another example includes compounds having the Formula (IIIo): 
wherein
Y is hydrogen, hydroxy, CH3, CN, CO2R, optionally substituted aryl, optionally substituted aryloxy, optionally substituted arylthioxy, optionally substituted aroyl, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, optionally substituted heterocyclic group, optionally substituted heterocycloxy, optionally substituted heteroaryl, optionally substituted heteroaryloxy, optionally substituted cycloalkyl group, optionally substituted cycloalkoxy group, amino, amido, ureido, or guanidino;
Y1 is hydrogen, alkyl, hydroxyalkyl, optionally substituted aralkyl, an optionally substituted aryl, aminoalkyl, amidoalkyl, ureidoalkyl, or guanidinoalkyl; and
n is 0, 1, 2, 3, 4, 5 or 6.
Compounds having Formula IIIo may be prepared according to Scheme 14. 
Particular examples of compounds having Formula III include: 
wherein n is 0, 1, 2, 3, 4, 5 or 6; 
Method of Harper and Powers, Biochemistry 24:7200-7213 (1985).
Additional compounds having Formula III include 4-benzyl-1-(3-hydroxy-1-methylpropyl)piperidine, 4-benzyl-1-(2-hydroxyethyl)piperidine, 1-benzyl-3-hydroxy-3-phenylpiperidine, 3-hydroxy-3-phenyl-1-phenethylpiperi-dine, 3-hydroxy-3-phenyl-1-(phenylpropyl)piperidine, and 4-benzoyl-1-(3-hydroxypropyl)piperidine.
Examples of compounds having Formula IV include those having the Formula (IVa): 
wherein
R1-R5 are independently hydrogen, halo, haloalkyl, aryl, fused aryl, a heterocyclic group, a heteroaryl group, alkyl, alkenyl, alkynyl, arylalkyl, arylalkenyl, arylalkynyl, hydroxyalkyl, nitro, amino, cyano, acylamido, hydroxy, thiol, acyloxy, azido, alkoxy, carboxy, carbonylamido, or alkylthiol;
n is 1, 2, 3, 4, 5, or 6;
Y is optionally substituted aryl, optionally substituted aryloxy, SAr, COAr, hydrogen, hydroxy, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, a heterocyclic group, a heteroaryl group, a cycloalkyl group, an amino group, an amido group, a ureido group, or a guanidino group; and
Y1 is hydrogen, alkyl, hydroxyalkyl, an optionally substituted aralkyl group, an optionally substituted aryl group, an aminoalkyl group, an amidoalkyl group, a ureidoalkyl group, or a guanidinoalkyl group.
Another example includes compounds having the Formula (IVb): 
wherein
R1-R5, n, Y and Y1 are the same described in formula IVa.
Compounds having Formula IV may be prepared by reaction of the corresponding piperidone with a Wittig reagent derived from a benzyl bromide. Alternatively, a benzyl grignard reagent may be reacted with the piperidone to give the hydroxybenzyl piperidine which may be dehydrated with sulfuric acid and heat.
Particular examples of compounds having Formula IV include 1-benzyl-4-(m-fluorobenzylidene)piperidine, 1-(3-hydroxypropyl)-4-benzylidenepiperidine, and 1-hexyl-4-benzylidenepiperidine.
Compounds having Formula V may be prepared according to Scheme 16 followed by reaction with one of the electrophiles mentioned above. 
See, Cook et al., J. Ned. Chem. 38:754 (1995).
An example of compounds having Formula V include: 
Compounds having Formula VI may be prepared according to Scheme 17. 
By varying the choice of the amine nucleophile, one can synthesize a family of amidines including the following: 
Compounds having Formula VII may be prepared according to Scheme 18. 
Examples of compounds having Formula VII include: 
Compounds having Formula VIII may be prepared according to Scheme 19. 
Examples of compounds having Formula VIII include: 
Compounds having Formula IX may be prepared according to Scheme 20. 
See, Iwasaki, N., et al., J. Med. Chem 38:496 (1995), who describe a variety of substituents in the 7-, 8- and 9-positions including fluoro, chloro, methoxy and nitro on the top left benzene ring.
Compounds having Formula X may be prepared according to Scheme 21. 
Compounds having Formula XI may be prepared according to Scheme 22. 
Compounds having Formula XII may be prepared by reaction of the corresponding 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imines with one of the electrophilic reagents listed above. Methods for preparing the starting 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imines are disclosed in U.S. Pat. No. 4,399,141, the disclosure of which is fully incorporated by reference herein.
Particular examples of compounds having Formula XIII include those having the Formula (XIIIa): 
wherein
Y is hydrogen, hydroxy, CH3, CN, CO2R, optionally substituted aryl, optionally substituted aryloxy, optionally substituted arylthioxy, optionally substituted aroyl, xe2x89xa1xe2x80x94Y1, xe2x95x90xe2x80x94Y1, optionally substituted heterocyclic group, optionally substituted heterocycloxy, optionally substituted heteroaryl, optionally substituted heteroaryloxy, optionally substituted cycloalkyl group, optionally substituted cycloalkoxy group, amino, amido, ureido, or guanidino; Y1 is hydrogen, alkyl, hydroxyalkyl, optionally substituted aralkyl, an optionally substituted aryl, aminoalkyl, amidoalkyl, ureidoalkyl, or guanidinoalkyl; and
n is 0, 1, 2, 3, 4, 5, or 6.
Compounds having Formula XIII may be prepared by reaction of the corresponding 10,5-(iminomethano)-10,11-dihydro-5H-dibenzo[a,d]-cycloheptenes (IDDCs) with one of the electrophilic reagents listed above. Methods for preparing the starting IDDCs are disclosed in U.S. Pat. No. 5,011,834, the disclosure of which is fully incorporated by reference herein.
Particular examples of compounds having Formula XIV include those having the Formula (XIVa): 
wherein
Y, Y1 and n are the same as described for formula XIIIa.
Another example includes those having the Formula (XIVb): 
wherein
Y, Y1 and n are the same as described in formula XIIIa.
Another example includes those compounds having the Formula (XIVc): 
wherein
Y, Y1 and n are the same as described in formula XIIIa.
Compounds having Formula XIV may be prepared as shown in Scheme 23. These compounds may be derived from guvacine or 4-hydroxynipecotic acid and reacted with one of the electrophiles listed above to give the desired product. 
RBI is Research Biochemicals International, Inc.
Compounds having Formula XV may be prepared by reaction of an appropriate nitrogen electrophile with a suitable electrophile XEY. Particular examples of compounds having Formula XV are 
Examples of compounds of Formula XVI include those having the Formula (XVIa): 
wherein
Y1 is (CHR2)n wherein n is 0, 1, 2, 3 or 4; and
Ar1, X, U and R2 are as previously described by Formula XVI.
Other examples include those having Formula (XVIb): 
wherein
V is (CH2)q wherein q is 1, 2 or 3 and
Ar1, X, U, Y and Z are previously described for Formula XVI.
The N-(hydroxyalkyl)piperidines of Formula XVI are selective antagonists of the NR1A/NR2B subtype NMDA receptors. They have good in vivo activity and some have a long half life in vivo. These compounds have relatively low activity at the alpha 1 receptor and therefore potentially have an enhanced side effect profile. In addition the compounds of Formula XVI have good water solubility which is advantageous for formulating an aqueous solution for iv adminstration.
Examples of compounds of Formula XVII include those having the Formula (XVIIa): 
wherein
Ar1, X, U, Z and Y are as previously described for Formula XVII.
Certain of the compounds of the present invention are expected to be potent anticonvulsants in animal models and will prevent ischemia-induced nerve cell death in the gerbil global ischemia model after administration.
The compounds of the present invention are active in treating or preventing neuronal loss, neurodegenerative diseases, chronic pain, are active as anticonvulsants and inducing anesthesia. They are also useful for treating epilepsy and psychosis. The therapeutic and side effect profiles of subunit-selective NMDA receptor antagonists and agonists should be markedly different from the more non-selective types of inhibitors. The subtype-selective ligands of the present invention are expected to exhibit little or no untoward side effects caused by non-selective binding with other receptors, particularly, the PCP and glutamate binding sites associated with the NMDA receptor. In addition, selectivity for different NMDA receptor subtypes will reduce side effects such as sedation that are common to non-subtype-selective NMDA receptor antagonists. The compounds of the present invention are effective in treating or preventing the adverse consequences of the hyperactivity of the excitatory amino acids, e.g., those that are involved in the NMDA receptor system, by preventing the ligand-gated cation channels from opening and allowing excessive influx of Ca++ into neurons, as occurs during ischemia.
Neurodegenerative diseases that may be treated with the compounds of the present invention include those selected from the group consisting of Alzheimer""s disease, amyotrophic lateral sclerosis, Huntington""s disease, Parkinson""s disease and Down""s syndrome.
The compounds of the present invention find particular utility in the treatment or prevention of neuronal loss associated with multiple strokes which give rise to dementia. After a patient has been diagnosed as suffering from a stroke, the compounds of the present invention may be administered to ameliorate the immediate ischemia and prevent further neuronal damage that may occur from recurrent strokes.
Moreover, the compounds of the present invention are able to cross the blood/brain barrier, which makes them particularly useful for treating or preventing conditions involving the central nervous system.
The compounds of the invention find particular utility in treating or preventing the adverse neurological consequences of surgery. For example, coronary bypass surgery requires the use of heart-lung machines, which tend to introduce air bubbles into the circulatory system that may lodge in the brain. The presence of such air bubbles robs neuronal tissue of oxygen, resulting in anoxia and ischemia. Pre- or post-surgical administration of the compounds of the present invention will treat or prevent the resulting ischemia. In a preferred embodiment, the compounds of the invention are administered to patients undergoing cardiopulmonary bypass surgery or carotid endarterectomy surgery.
The compounds of the present invention also find utility in treating or preventing chronic pain. Such chronic pain may be the result of surgery, trauma, headache, arthritis, pain from terminal cancer or degenerative diseases. The compounds of the present invention also find particular utility in the treatment of phantom pain that results from amputation of an extremity. In addition to treatment of pain, the compounds of the invention are also expected to be useful in inducing anesthesia, either general or local anesthesia, for example, during surgery.
The subunit-selective NMDA receptor antagonists, agonists and modulators may be tested for in vivo anticonvulsant activity after iv or ip injection using a number of anticonvulsant tests in mice (audiogenic seizure model in DBA-2 mice, pentylenetetrazol-induced seizures in mice, maximum electroshock seizure test (MES) or NMDA-induced death). The compounds may also be tested in drug discrimination tests in rats trained to discriminate PCP from saline. It is expected that most of the compounds of the present invention will not generalize to PCP at any dose. In addition, it is also expected that none of the compounds will produce a behavioral excitation in locomotor activity tests in the mouse. It is expected that such results will suggest that the subunit-selective NMDA receptor antagonists and agonists of the present invention do not show the PCP-like behavioral side effects that are common to NMDA channel blockers such as MK-801 and PCP or to competitive NMDA antagonists such as CGS 19755.
The subunit-selective NMDA receptor antagonists and agonists are also expected to show potent activity in vivo after intraperitoneal injection suggesting that these compounds can penetrate the blood/brain barrier.
Elevated levels of glutamate has been associated with glaucoma. In addition, it has been disclosed that glaucoma management, particularly protection of retinal ganglion cells, can be achieved by administering to a patient a compound capable of reducing glutamate-induced excitotoxicity in a concentration effective to reduce the excitotoxicity. See WO94/13275. Thus, the compounds of the present invention, which are expected to cross the blood-retina barrier, are also expected to be useful in the treatment of glaucoma. Preferably, the invention is directed to the treatment of patients which have primary open-angle glaucoma, chronic closed-angle glaucoma, pseudo doexfoliation, or other types of glaucoma or ocular hypertension. Preferably, the compound is administered over an extended period (e.g. at least six months and preferably at least one year), regardless of the changes in the patient""s intraocular pressure over the period of administration.
The compounds of the present invention are also useful in treating CMV retinitis, particularly in combination with antiviral agents. CMV afflicts the ganglion cell layer which may result in higher levels of glutamate. Thus, NMDA receptor antagonists could block retinitis by blocking the toxicity effect of high level of glutamate.
Aminoglycoside antibiotics have been used successfully in the treatment of serious Gram-negative bacterial infections. However, prolonged treatment with these antibiotics will result in the destruction of sensory hearing cells of the inner ear and consequently, induce permanent loss of hearing. A recent study of Basile, et al. (Nature Medicine, 2: 1338-1344, 1996) indicated that aminoglycosides produce a polyamine-like enhancement of glutamate excitotoxicity through their interaction with the NMDA receptor. Thus, compounds of the present invention with NMDA receptor antagonist activity will be useful in preventing aminoglycoside antibiotics-induced hearing loss by antagonizing their interaction with the receptor.
The compounds of the present invention are useful in treating headaches, in particular, migraine headaches. During migraine attack, a sensory disturbance with unique changes of brain blood flow will result in the development of characteristic migraine auras. Since this unique phenomena has been replicated in animal experiments with cortical-spreading depression (CSD) of Leao, A.A.P.J., Neurophysiol. 7:359-390 (1944), CSD is considered an important phenomena in the pathophysiology of migraine with aura (Tepley et al., In: Biomagnetism, eds. S. Williamson, L. Kaufmann, pp. 327-330, Plenum Press, New York (1990)). The CSD is associated with the propagation (2xcx9c6 mm/s) of transient changes in electrical activity which relate to the failure of ion homoestatis in the brain, efflux of excitatory amino acids from the neurons and increased energy metabolism (Lauritzen, M., Acta Neurol. Scand. 76 (Suppl. 113):4-40 (1987)). It has been demonstrated that the initiation of CSD in a variety of animals, including humans, involved the release of glutamate and could be triggered by NMDA (Curtis et al., Nature 191:1010-1011 (1961); and Lauritzen et al., Brain Res. 475:317-327 (1988)). Subtype selective NMDA antagonists will be therapeutically useful for migraine headache because of their expected low side effects, their ability to cross the blood brain barrier and their systemic bioavailability.
Bladder activity is controlled by parasympathetic preganglionic neurons in the sacral spinal cord (DeGroat et al., J. Auton. Nerv. Sys. 3:135-160(1981)). In humans, it has been shown that the highest density of NMDA receptors in the spinal cord are located at the sacral level, including those areas that putatively contain bladder parasympathetic preganglionic neurons (Shaw et al., Brain Research 539:164-168 (1991)). Because NMDA receptors are excitatory in nature, pharmacological blockade of these receptors would suppress bladder activity. It has been shown that the noncompetitive NMDA receptor antagonist MK801 increased the frequency of micturition in rat (Vera and Nadelhaft, Neuroscience Letters 134:135-138(1991)). In addition, competitive NMDA receptor antagonists have also been shown to produce a dose-dependent inhibition of bladder and of urethral sphincter activity (U.S. Pat. No. 5,192,751). Thus, it is anticipated that subtype-selective NMDA receptor antagonists will be effective in the treatment of urinary incontinence mediated by their modulation on the receptor channel activity.
Non-competitive NMDA receptor antagonist MK801 has been shown to be effective in a variety of animal models of anxiety which are highly predictive of human anxiety (Clineschmidt, B. V. et al., Drug Dev. Res. 2:147-163 (1982)). In addition, NMDA receptor glycine site antagonists are shown to be effective in the rat protentiated startle test (Anthony, E. W., Eur. J. Pharmacol. 250:317-324 (1993)) as well as several other animal anxiolytic models (Winslow, J. et al, Eur. J. Pharmacol. 190:11-22 (1990); Dunn, R. et al., Eur. J. Pharmacol. 214:207-214 (1992); and Kehne, J. H. et al, Eur. J. Pharmacol. 193:282-292 (1981)).
Glycine site antagonists, (+) HA-966 and 5,7-dichlorokynurenic acid were found to selectively antagonize d-amphetamine induced stimulation when injected into rat nucleus accumbens but not in striatum (Hutson, P. H. et al., Br. J. Pharmacol. 103:2037-2044 (1991)). Interestingly, (+) HA-966 was also found to block PCP and MK801-induced behavioral arousal (Bristow, L. J. et al., Br. J. Pharmacal, 108:1156-1163 (1993)). These findings suggest that a potential use of NMDA receptor channel modulators, but not channel blockers, as atypical neuroleptics.
It has been shown that in an animal model of Parkinson""s diseasexe2x80x94MPP+or methamphetamine-induced damage to dopaminergic neuronsxe2x80x94can be inhibited by NMDA receptor antagonists (Rojas et al., Drug Dev. Res. 29:222-226 (1993); and Sonsalla et al, Science 243;398-400 (1989)). In addition, NDMA receptor antagonists have been shown to inhibit haloperidol-induced catalepsy (Schmidt, W. J. et al., Amino Acids 1:225-237 (1991)), increase activity in rodents depleted of monoamines (Carlsson et al., Trends Neurosci. 13:272-276 (1990)) and increase ipsilateral rotation after unilateral substantia nigra lesion in rats (Snell, L. D. et al., J. Pharmacol. Exp. Ther. 235:50-57 (1985)). These are also experimental animal models of Parkinson""s disease. In animal studies, the antiparkinsonian agent amantadine and memantine showed antiparkinsonian-like activity in animals at plasma levels leading to NMDA receptor antagonism (Danysz, W. et al., J. Neural Trans. 7:155-166, (1994)). Thus, it is possible that these antiparkinsonian agents act therapeutically through antagonism of an NMDA receptor. Therefore, the balance of NMDA receptor activity maybe important for the regulation of extrapyramidal function relating to the appearance of parkinsonian symptoms.
It is well known to use opiates, e.g., morphine, in the medical field to alleviate pain. (As used herein, the term xe2x80x9copiatesxe2x80x9d is intended to mean any preparation or derivative of opium, especially the alkaloids naturally contained therein, of which there are about twenty, e.g., morphine, noscapine, codeine, papaverine, and thebaine, and their derivatives.) Unfortunately, with continued use, the body builds up a tolerance for the opiate, and, thus, for continued relief, the patient must be subjected to progressively larger doses. Tolerance develops after both acute and chronic morphine administration (Kornetsky et al., Science 162:1011-1012 (1968); Way et al., J. Pharmacol. Exp Ther. 167:1-8 (1969); Huidobro et al., J. Pharmacol. Exp Ther. 198:318-329 (1976); Lutfy et al., J. Pharmacol. Exp Ther. 256:575-580 (1991)). This, in itself, can be detrimental to the patient""s health. Furthermore, a time can come when the tolerance is substantially complete and the pain killing properties of the drug are no longer effective. Additionally, administration of higher doses of morphine may lead to respiratory depression, causing the patient to stop breathing. Seeking alternative drugs to produce analgesia without development of tolerance or as an adjunct therapy to block tolerance without interference with analgesia is an active area of research.
Recent studies have suggested a modulatory role for the NMDA receptor in morphine tolerance. (Trujillo et al., Science 251:85-87 (1991); Marek et al., Brain Res. 547:77-81 (1991); Tiseo et al., J. Pharmacol. Exp Ther. 264:1090-1096 (1993); Lutfy et al., Brain Res. 616:83-88 (1993); Herman et al., Neuropsychopharmacology 12:269-294 (1995).) Further, it has been reported that NMDA receptor antagonists are useful for inhibiting opioid tolerance and some of the symptoms of opioid withdrawal. Thus, the present invention is also directed to the administration of the compounds described herein to inhibit opiate tolerance and to treat or ameliorate the symptoms of opiate withdrawal by blocking the glycine co-agonist site associated with the NMDA receptor.
Thus, the present invention is directed to compounds having high binding to a particular NMDA receptor subunit and low binding to other sites such as dopamine and other catecholamine receptors, and "sgr" sites. According to the present invention, those compounds having high binding to a particular NMDA subunit exhibit an IC50 of about 100 xcexcM or less in an NMDA subunit binding assay (see the Examples). Preferably, the compounds of the present invention exhibit an IC50 of 10 xcexcM or less. Most preferably, the compounds of the present invention exhibit an IC50 of about 1.0 xcexcM or less.
The efficacy of the NMDA subunit selective antagonists to inhibit glutamate neurotoxicity in rat brain cortex neuron cell culture system may be determined as follows. An excitotoxicity model modified after that developed by Choi (Choi, D. W., J. Neuroscience 7:357 (1987)) may be used to test anti-excitotoxic efficacy of the antagonists. Fetuses from rat embryonic day 19 are removed from time-mated pregnant rats. The brains are removed from the fetuses and the cerebral cortex is dissected. Cells from the dissected cortex are dissociated by a combination of mechanical agitation and enzymatic digestion according to the method of Landon and Robbins (Methods in Enzymology 124:412 (1986)). The dissociated cells are passed through an 80 micron nitex screen and the viability of the cells are assessed by Trypan Blue. The cells are plated on poly-D-lysine coated plates and incubated at 37xc2x0 C. in an atmosphere containing 91% O2/9% CO2. Six days later, fluoro-d-uracil is added for two days to suppress non-neural cell growth. At culture day 12, the primary neuron cultures are exposed to 100 xcexcM glutamate for 5 minutes with or without increasing doses of antagonist or other drugs. After 5 minutes the cultures are washed and incubated for 24 hours at 37xc2x0 C. Neuronal cell damage is quantitated by measuring lactate dehydrogenase (LDH) activity that is released into the culture medium. The LDH activity is measured according to the method of Decker et al. (Decker et al., J. Immunol. Methods 15:16 (1988)).
The anticonvulsant activity of the antagonists may be assessed in the audiogenic seizure model in DBA-2 mice as follows. DBA-2 mice may be obtained from Jackson Laboratories, Bar Harbor, Me. These mice at an age of  less than 27 days develop a tonic seizure within 5-10 seconds and die when they are exposed to a sound of 14 kHz (sinus wave) at 110 dB (Lonsdale, D., Dev. Pharmacol. Ther. 4:28 (1982)). Seizure protection is defined when animals injected with drug 30 minutes prior to sound exposure do not develop a seizure and do not die during a 1 minute exposure to the sound. 21 day old DBA-2 mice are used for all experiments. Compounds are given intraperitoneally in either saline, DMSO or polyethyleneglycol-400. Appropriate solvent controls are included in each experiment. Dose response curves are constructed by giving increasing doses of drug from 1 mg/kg to 100 mg/kg. Each dose group (or solvent control) consists of at least six animals.
The anticonvulsant efficacy of the antagonists may be assessed in the pentylenetetrazol (PTZ)-induced seizure test as follows. Swiss/Webster mice, when injected with 50 mg/kg PTZ (i.p.) develop a minimal clonic seizure of approximately 5 seconds in length within 5-15 minutes after drug injection. Anticonvulsant efficacy of an antagonist (or other) drug is defined as the absence of a seizure when a drug is given 30 minutes prior to PTZ application and a seizure does not develop for up to 45 minutes following PTZ administration. The antagonist or other drugs are given intraperitoneally in either saline, DMSO or polyethyleneglycol-400. Appropriate solvent controls are included in each experiment. Dose response curves are constructed by giving increasing doses of drug from 1 mg/kg to 100 mg/kg. Each dose group (or solvent control) consists of at least six animals.
The efficacy of NMDA antagonists to protect mice from NMDA induced death may be assessed as follows. When mice are injected with 200 mg/kg N-methyl-D-aspartate (NMDA) i.p., the animals will develop seizures followed by death within 5-10 minutes. The antagonists are tested for their ability to prevent NMDA-induced death by giving the drugs i.p. 30 minutes prior to the NMDA application. The antagonist or other drugs are given intraperitoneally in either saline, DMSO or polyethyleneglycol-400. Appropriate solvent controls are included in each experiment. Dose response curves are constructed by giving increasing doses of drug from 1 mg/kg to 100 mg/kg. Each dose group (or solvent control) consists of at least six animals.
The series of different evaluations may be conducted on doses of the NMDA antagonists of the invention to determine the biological activity of the compounds both in normal gerbils and in animals exposed to 5 minutes of bilateral carotid occlusion. See Scheme 24. 
These studies are conducted in animals who are conscious and have no other pharmacological agents administered to them. Gerbils are preinstrumented 48-hours prior to ischemia to allow for the complete elimination of the pentobarbital anesthetic which is employed. When tested with drugs, animals are given IP injections of the NMDA antagonist or vehicle. In the case of multiple injections, animals are given IP injections 2 hours apart and the final injection is given 30 minutes prior to the ischemic period or in the case of post treatment, the animals are given injections at 30 minutes, 2 hours, 4 hours and 6 hours post-ischemic reperfusion.
In order to assess the direct pharmacological activity or potential activity of the NMDA antagonists, naive gerbils are injected with either saline or differing doses of the antagonist. The behavioral changes are assessed using a photobeam locomotor activity chamber which is a two foot circular diameter arena with photobeam detection. Animals are individually placed in the 2 foot diameter chambers. The chambers are housed in a cabinet which is closed and noise is abated using both a background white noise generator and a fan. Animals are placed in these chambers in the case of the initial pharmacological evaluation for a period of 6 hours and the total activity during each successive hour is accumulated using the computer control systems.
Saline results in an initial high rate of activity, with the control animals showing a first hour activity level of about 1600 counts. This level of control activity is typical for the gerbil under these experimental conditions. As the session progressed, animals decrease their exploratory activity and at the terminal period the activity declines to about 250 counts per hour. It is expected that the NMDA antagonists of the present invention will have no significant effect on either the initial exploratory rate or the terminal rate of exploration.
In a next phase of the evaluation of the NMDA antagonists, gerbils are pretreated with varying doses of the antagonists and then exposed to a five minute period of bilateral carotid occlusion. Following the initiation of reperfusion, animals are placed into the circular locomotor activity testing apparatus and the activity at the beginning of the first hour following reperfusion is monitored for the subsequent four hours.
Control animals not exposed to ischemia and given injections of saline prior to being placed in the locomotor activity chamber show a characteristic pattern of activity which in the first hour of locomotor activity is substantially higher than during all other hours and progressively declined over the four hours to a very low value. In contrast to the progressive decline in activity over the four hour testing period, control animals that are exposed to five minutes of cortical ischemia demonstrate a completely different pattern of locomotor activity. During the first hour there is a significant decline in activity, which is followed by a progressive increase in which the activity during the fourth hour is ten-fold higher than that demonstrated by animals not exposed to carotid occlusion. These results are typical and are a reliable result of the alterations caused by five minutes of bilateral carotid occlusion in the gerbil.
Separate groups of gerbils are pretreated with the NMDA antagonists of the invention 30 minutes before the onset of carotid occlusion and then placed into the locomotor activity following one hour of reperfusion. It is expected that pretreatment of the gerbils with the NMDA antagonists of the invention will prevent both the post-ischemic decrease and increase in activity. Post-ischemic decreases in activity are expected to be near zero during the first hour following reperfusion. Pretreatment with the NMDA antagonists of the invention is expected to reduce or prevent this early depression of behavior. In addition, the NMDA antagonists of the invention are expected to prevent the post-ischemic stimulation of behavior. Subsequent to completion of the single dose pretreatment evaluations, gerbils are also evaluated with multiple injections of the NMDA antagonists of the invention. Doses are administered I.P. at 6 hours, 4 hours, 2 hours and 30 minutes prior to the onset of 5 minutes of ischemia.
At 24 hours all animals are evaluated for differences in patrolling behavior using a 8-arm radial maze. In this procedure, animals are placed into the center start chamber of the maze, the barrier removed and the amount of time and the number of times the animal makes an error recorded prior to completion of exploration in all 8 arms of the maze. An error is defined as the revisiting of an arm by entering to the extent of the entire body without including tail by the animal. If the animal perseveres or fails to leave the arm for longer than five minutes, the session is terminated. In the control population of the animals, the number of errors and exploration of the maze with no prior experience (naive) is approximately 6 errors. This is an average value for an N of 28 gerbils. Following 5 minutes of bilateral carotid occlusion and testing at 24 hours, gerbils make an average number of errors of 21. When animals are pretreated with the NMDA antagonists of the invention, there is expected to be a significant reduction in the number of errors made.
There is also expected to be a significant sparing of the behavioral changes that are induced in the radial arm maze performance.
It is also expected that post treatment with the NMDA antagonists of the invention will reduce the short term memory impairment 24 hours post ischemic/reperfusion.
The effects of 5 minutes of bilateral carotid occlusion on neuronal cell death in the dorsal hippocampus may be evaluated in animals 7 days after ischemia reperfusion injury. Previous studies have demonstrated that neuronal degeneration begins to occur around 3 days following cerebral ischemia. By 7 days, those neurons that have been affected will undergo cytolysis and have either completed degeneration or are readily apparent as dark nuclei and displaced nuclei or as cells with eosinophilic cytoplasm and pycnotic nuclei. The lesion with 5 minutes of ischemia is essentially restricted within the hippocampus to the CA1 region of the dorsal hippocampus. The intermedial lateral zone of the horn is unaffected and the dentate gyrus and/or in CA3 do not show pathology. Gerbils are anesthetized on day 7 following ischemia with 60 mg/kg of pentobarbital. Brains are perfused transcardiac with ice-cold saline followed by buffered paraformaldehyde (10%). Brains are removed, imbedded and sections made. Sections are stained with hematoxylin-eosin and neuronal cell counts are determined in terms of number of neuronal nuclei/100 micrometers. Normal control animals (not exposed to ischemia reperfusion injury) will not demonstrate any significant change in normal density nuclei within this region. Exposure to five minutes of bilateral carotid occlusion results in a significant reduction in the number of nuclei present in the CA1 region. In general, this lesion results in a patchy necrosis instead of a confluent necrosis, which is seen if 10 minutes of ischemia is employed. Pretreatment with the NMDA antagonists of the invention are expected to produce a significant protection of hippocampal neuronal degeneration.
It is known that NMDA receptors are critically involved in the development of persistent pain following nerve and tissue injury. Tissue injury such as that caused by injecting a small amount of formalin subcutaneously into the hindpaw of a test animal has been shown to produce an immediate increase of glutamate and aspartate in the spinal cord (Skilling, S. R., et al., J. Neurosci. 10:1309-1318 (1990)). Administration of NMDA receptor blockers reduces the response of spinal cord dorsal horn neurons following formalin injection (Dickenson and Aydar, Neuroscience Lett. 121:263-266 (1991); Haley, J. E., et al., Brain Res. 518:218-226 (1990)). These dorsal horn neurons are critical in carrying the pain signal from the spinal cord to the brain and a reduced response of these neurons is indicative of a reduction in pain perceived by the test animal to which pain has been inflicted by subcutaneous formalin injection.
Because of the observation that NMDA receptor antagonists can block dorsal horn neuron response induced by subcutaneous formalin injection, NMDA receptor antagonists have potential for the treatment of chronic pain such as pain that is caused by surgery or by amputation (phantom pain) or by infliction of other wounds (wound pain). However, the use of conventional NMDA antagonists such as MK-801 or CGS 19755, in preventing or treating chronic pain, is severely limited by the adverse PCP-like behavioral side effects that are caused by these drugs. It is expected that the NMDA receptor antagonists that are the subject of this invention will be highly effective in preventing chronic pain in mice induced by injecting formalin subcutaneously into the hindpaw of the animals. Because the NMDA receptor antagonists of this invention are expected to be free of PCP-like side effects, these drugs are highly useful in preventing or treating chronic pain without causing PCP-like adverse behavioral side effects.
The effects of the NMDA receptor antagonists of the present invention on chronic pain may be evaluated as follows. Male Swiss/Webster mice weighing 25-35 grams are housed five to a cage with free access to food and water and are maintained on a 12 hour light cycle (light onset at 0800 h). The NMDA receptor antagonist is dissolved in DMSO at a concentration of 1-40 and 5-40 mg/mL, respectively. DMSO is used as vehicle control. All drugs are injected intraperitoneally (1 xcexcL/g). The formalin test is performed as described (Dubuisson and Dennis, Pain 4:H161-174 (1977)). Mice are observed in a plexiglass cylinder, 25 cm in diameter and 30 cm in height. The plantar surface of one hindpaw is injected subcutaneously with 20 xcexcL of 5% formalin. The degree of pain is determined by measuring the amount of time the animal spends licking the formalin-injected paw during the following time intervals: 0-5xe2x80x2 (early phase); 5xe2x80x2-10xe2x80x2, 10xe2x80x2-15xe2x80x2 and 15xe2x80x2-50xe2x80x2 (late phase). To test whether the NMDA receptor antagonists prevent chronic pain in the test animals, vehicle (DMSO) or drugs dissolved in vehicle at doses of 1 mg/kg to 40mg/kg are injected intraperitoneally 30 minutes prior to the formalin injection. For each dose of drug or vehicle control at least six animals are used.
Compared to vehicle control, it is expected that the intraperitoneal injection of the NMDA receptor antagonists 30 minutes prior to formalin injection into the hindpaw will significantly inhibit formalin-induced chronic pain in a dose-dependent manner as determined by the reduction of the time spent licking by the mouse of the formalin injected hindpaw caused by increasing doses of NMDA receptor antagonist.
Compositions within the scope of this invention include all compositions wherein the compounds of the present invention are contained in an amount which is effective to achieve its intended purpose. While individual needs vary, determination of optimal ranges of effective amounts of each component is within the skill of the art. Typically, the compounds may be administered to mammals, e.g., humans, orally at a dose of 0.0025 to 50 mg/kg, or an equivalent amount of the pharmaceutically acceptable salt thereof, per day of the body weight of the mammal being treated for anxiety disorders, e.g., generalized anxiety disorder, phobic disorders, obsessional compulsive disorder, panic disorder, and post traumatic stress disorders or for schizophrenia or other psychoses. Preferably, about 0.01 to about 10 mg/kg is orally administered to treat or prevent such disorders. For intramuscular injection, the dose is generally about one-half of the oral dose. For example, for treatment or prevention of anxiety, a suitable intramuscular dose would be about 0.0025 to about 15 mg/kg, and most preferably, from about 0.01 to about 10 mg/kg.
In the method of treatment or prevention of neuronal loss in ischemia, brain and spinal cord trauma, hypoxia, hypoglycemia, and surgery, to treat or prevent glaucoma or urinary incontinence, as well as for the treatment of Alzheimer""s disease, amyotrophic lateral sclerosis, Huntington""s disease, Parkinson""s disease and Down""s Syndrome, or in a method of treating a disease in which the pathophysiology of the disorder involves hyperactivity of the excitatory amino acids or NMDA receptor-ion channel related neurotoxicity, the pharmaceutical compositions of the invention may comprise the compounds of the present invention at a unit dose level of about 0.01 to about 50 mg/kg of body weight, or an equivalent amount of the pharmaceutically acceptable salt thereof, on a regimen of 1-4 times per day. When used to treat chronic pain, migrain headache, to induce anesthesia, to treat or prevent opiate tolerance or to treat opiate withdrawal, the compounds of the invention may be administered at a unit dosage level of from about 0.01 to about 50 mg/kg of body weight, or an equivalent amount of the pharmaceutically acceptable salt thereof, on a regimen of 1-4 times per day. Of course, it is understood that the exact treatment level will depend upon the case history of the animal, e.g., human being, that is treated. The precise treatment level can be determined by one of ordinary skill in the art without undue experimentation.
The unit oral dose may comprise from about 0.01 to about 50 mg, preferably about 0.1 to about 10 mg of the compound. The unit dose may be administered one or more times daily as one or more tablets each containing from about 0.1 to about 10, conveniently about 0.25 to 50 mg of the compound or its solvates.
In addition to administering the compound as a raw chemical, the compounds of the invention may be administered as part of a pharmaceutical preparation containing suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries which facilitate processing of the compounds into preparations that can be used pharmaceutically. Preferably, the preparations, particularly those preparations that can be administered orally and that can be used for the preferred type of administration, such as tablets, dragees, and capsules, and also preparations that can be administered rectally, such as suppositories, as well as suitable solutions for administration by injection or orally, contain from about 0.01 to 99 percent, preferably from about 0.25 to 75 percent of active compound(s), together with the excipient.
Also included within the scope of the present invention are the non-toxic pharmaceutically acceptable salts of the compounds of the present invention. Acid addition salts are formed by mixing a solution of the particular NMDA subunit selective antagonist or agonist of the present invention with a solution of a pharmaceutically acceptable non-toxic acid such as hydrochloric acid, fumaric acid, maleic acid, succinic acid, acetic acid, citric acid, tartaric acid, carbonic acid, phosphoric acid, oxalic acid, and the like. Basic salts are formed by mixing a solution of the particular haloperidol analog of the present invention with a solution of a pharmaceutically acceptable non-toxic base such as sodium hydroxide, potassium hydroxide, choline hydroxide, sodium carbonate and the like.
The pharmaceutical compositions of the invention may be administered to any animal which may experience the beneficial effects of the compounds of the invention. Foremost among such animals are mammals, e.g., humans, although the invention is not intended to be so limited.
The pharmaceutical compositions of the present invention may be administered by any means that achieve their intended purpose. For example, administration may be by parenteral, subcutaneous, intravenous, intramuscular, intraperitoneal, transdermal, or buccal routes. Alternatively, or concurrently, administration may be by the oral route. The dosage administered will be dependent upon the age, health, and weight of the recipient, kind of concurrent treatment, if any, frequency of treatment, and the nature of the effect desired.
The pharmaceutical preparations of the present invention are manufactured in a manner that is itself known, for example, by means of conventional mixing, granulating, dragee-making, dissolving, or lyophilizing processes. Thus, pharmaceutical preparations for oral use can be obtained by combining the active compounds with solid excipients, optionally grinding the resulting mixture and processing the mixture of granules, after adding suitable auxiliaries, if desired or necessary, to obtain tablets or dragee cores.
Suitable excipients are, in particular, fillers such as saccharides, for example, lactose or sucrose, mannitol or sorbitol, cellulose preparations and/or calcium phosphates, for example, tricalcium phosphate or calcium hydrogen phosphate, as well as binders such as starch paste, using, for example, maize starch, wheat starch, rice starch, potato starch, gelatin, tragacanth, methyl cellulose, hydroxy-propylmethylcellulose, sodium carboxymethylcellulose, and/or polyvinyl pyrrolidone. If desired, disintegrating agents may be added such as the above-mentioned starches and also carboxymethyl-starch, cross-linked polyvinyl pyrrolidone, agar, or alginic acid or a salt thereof, such as sodium alginate. Auxiliaries are, above all, flow-regulating agents and lubricants, for example, silica, talc, stearic acid or salts thereof, such as magnesium stearate or calcium stearate, and/or polyethylene glycol. Dragee cores are provided with suitable coatings which, if desired, are resistant to gastric juices. For this purpose, concentrated saccharide solutions may be used, which may optionally contain gum arabic, talc, polyvinyl pyrrolidone, polyethylene glycol and/or titanium dioxide, lacquer solutions and suitable organic solvents or solvent mixtures. In order to produce coatings resistant to gastric juices, solutions of suitable cellulose preparations, such as, acetyl-cellulose phthalate or hydroxypropymethyl-cellulose phthalate, are used. Dye stuffs or pigments may be added to the tablets or dragee coatings, for example, for identification or in order to characterize combinations of active compound doses.
Other pharmaceutical preparations that can be used orally include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a plasticizer such as glycerol or sorbitol. The push-fit capsules can contain the active compounds in the form of granules, which may be mixed with fillers such as lactose, binders such as starches, and/or lubricants such as talc or magnesium stearate and, optionally, stabilizers. In soft capsules, the active compounds are preferably dissolved or suspended in suitable liquids, such as fatty oils, or liquid paraffin. In addition, stabilizers may be added.
Possible pharmaceutical preparations that can be used rectally include, for example, suppositories, which consist of a combination of one or more of the active compounds with a suppository base. Suitable suppository bases are, for example, natural or synthetic triglycerides, or paraffin hydrocarbons. In addition, it is also possible to use gelatin rectal capsules that consist of a combination of the active compounds with a base. Possible base materials include, for example, liquid triglycerides, polyethylene glycols, or paraffin hydrocarbons.
Suitable formulations for parenteral administration include aqueous solutions of the active compounds in water-soluble form, for example, water-soluble salts and alkaline solutions. In addition, suspensions of the active compounds as appropriate oily injection suspensions may be administered. Suitable lipophilic solvents or vehicles include fatty oils, for example, sesame oil, or synthetic fatty acid esters, for example, ethyl oleate or triglycerides or polyethylene glycol-400 (the compounds are soluble in PEG-400). Aqueous injection suspensions may contain substances that increase the viscosity of the suspension include, for example, sodium carboxymethyl cellulose, sorbitol, and/or dextran. Optionally, the suspension may also contain stabilizers.
The characterization of NMDA subunit binding sites in vitro has been difficult because of the lack of selective drug ligands. Thus, the NMDA ligands of the present invention may be used to characterize the NMDA subunits and their distribution. Particularly preferred NMDA subunit selective antagonists and agonists of the present invention that may be used for this purpose are isotopically radiolabelled derivatives, e.g., where one or more of the atoms are replaced with 3H, 11C, 14C, 15N, or 18F. Alternatively, a fluorescent group Y may be employed. Examples of such groups include 4-nitrobenzofurazan: 
The following examples are illustrative, but not limiting, of the method and compositions of the present invention. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in clinical therapy and that are obvious to those skilled in the art are within the spirit and scope of the invention.